Abstract
The co-culture of Cupriavidus necator DSM 428 and Pseudomonas citronellolis NRRL B-2504 was performed using apple pulp waste from the fruit processing industry as the sole carbon source to produce poly(3-hydroxybutyrate), P(3HB) and medium-chain length PHA, mcl-PHA, respectively. The polymers accumulated by both strains were extracted from the co-culture’s biomass, resulting in a natural blend that was composed of around 48 wt% P(3HB) and 52 wt% mcl-PHA, with an average molecular weight of 4.3 × 105 Da and a polydispersity index of 2.2. Two melting temperatures (Tm) were observed for the blend, 52 and 174 °C, which correspond to the Tm of the mcl-PHA and P(3HB), respectively. P(3HB)/mcl-PHA blend films prepared by the solvent evaporation method had permeabilities to oxygen and carbon dioxide of 2.6 and 32 Barrer, respectively. The films were flexible and easily deformed, as demonstrated by their tensile strength at break of 1.47 ± 0.07 MPa, with a deformation of 338 ± 19% until breaking, associated with a Young modulus of 5.42 ± 1.02 MPa. This study demonstrates for the first time the feasibility of using the co-culture of C. necator and P. citronellolis strains to obtain a natural blend of P(3HB)/mcl-PHA that can be processed into films suitable for applications ranging from commodity packaging products to high-value biomaterials.
Highlights
Polyhydroxyalkanoates (PHAs) are natural polyesters accumulated intracellularly by a variety of bacteria and Archaea, as carbon and energy storage compounds. These biopolymers have attracted great attention because they are obtained from renewable resources, are biodegradable and biocompatible, and present excellent material properties that range from rigid thermoplastics to flexible elastomers [1]
While glucose was completely consumed, only 2.5 g/L of the initial fructose available were metabolized during the run (Figure 1(A2))
Apple pulp waste from the fruit processing industry was successfully used as the sole carbon source for the co-culture of C. necator DSM 428 and P. citronellolis NRRL B-2504 to produce a natural P(3HB)/mcl-PHA blend
Summary
Polyhydroxyalkanoates (PHAs) are natural polyesters accumulated intracellularly by a variety of bacteria and Archaea, as carbon and energy storage compounds. These biopolymers have attracted great attention because they are obtained from renewable resources, are biodegradable and biocompatible, and present excellent material properties that range from rigid thermoplastics to flexible elastomers [1]. The material properties of PHAs can be tailored by choosing the appropriate producing bacteria and substrates [2,3] Given this set of characteristics, PHAs hold huge potential for use in a wide range of applications, including packaging and medical applications (such as in drug delivery or tissue engineering) [3,4]. The use of PHAs in the medical field is supported by the fact that in vivo, their degradation products, monomeric and oligomeric molecules, exert no toxic nor negative effects to human or animal cells or tissue [3,5]
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